A fuel cell is an electrochemical device that converts chemical energy into electric energy. A fuel cell is advantageous because it is highly efficient, emits no noxious fumes (as opposed to existing energy sources), and can use a variety of different fuels. Thus, fuel cells are considered to be a future energy source.
A fuel cell converts chemical energy, which is released by an oxidizing material such as LNG, LPG, methanol, etc., into electric energy through an electrochemical reaction. Fuel cells utilize hydrogen, which is easily generated from natural gas and atmospheric oxygen. The fuel cell can be used as a power source of a vehicle, replacing the existing internal-combustion engine in order to address problems such as increasing energy costs, environmental pollution, and warming of the earth.
A disadvantage of using fuel cells as a power source of a vehicle, however, is that they cannot generate enough power to drive a motor until after the motor is activated at an initial cold start. To compensate for this disadvantage, a hybrid vehicle is being developed that uses both a battery and a fuel cell, in some cases concurrently. These vehicles are typically referred to as fuel cell hybrid vehicles.
One problem with a fuel cell hybrid vehicle is that there is a danger that electromotive force generated from a motor during deceleration or shut-down of the vehicle will potentially flow into the fuel cell. To avoid this from occurring, conventional fuel cell hybrid vehicles use a simple contactor as a safety device between the fuel cell and the vehicle controller. No separate device for managing a specific voltage path supplying high voltage to the motor (i.e., a driving source) is provided.
Also, in a conventional fuel cell hybrid vehicle with a power connection unit, it is difficult to control polarity of the power supply unit through a control program. Controlling polarity is complex because the control program for the power connection unit must control a cathode (−) and an anode (+) of the power supply unit simultaneously, and the control program cannot determine whether the power supplied to the motor is power from the fuel cell or power from the battery.